wave wrote on Oct 31st, 2011, 1:42pm:Arg! I'm seeing several incorrect statements today.
Loose E is correct.
You need Resistors in parallel with the Caps for a DC sense point and DC feedback.
Raja - there IS a difference. Without a constant bias, it may never startup. If your DC bias point (broken already) is at a place where Loopgain = 0, you have no CMFB regulation.
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Wave
OK !! So your statement is without resisitor one can NOT sense CM voltage then how things work in SWITCH CAP CMFB circuit.
By the way the above circuits are the snapshot of one state of SWITCH CAP sense circuit
One thing to mention, even if you give constant current source bias CMFB start-up will still exist if you solely consider only the CKT shown above !!
For your information, there is no difference between a resistive divider (R1 & R2) and a CAPCACITIVE Voltage divider (provided you have control on the initial condition of the CAPs which generally happens in CAP-CMFB circuit).
For Res case Vout=Vin[R2/(R1+R2)] & for CAP case Vout =Vin[C1/(C1+C2)]
!!!